Variable capacitors

ABSTRACT

In the variable capacitors of the coaxial type where a tubular electrode is moved by screw or similar action to engage more or less a stationary electrode, and dielectric is between the electrodes, a spring-stressed means is provided to establish direct contact between the movable electrode and a circuit, which said spring-stressed means can be also the rotation restraining element and the positive stop for the movable electrode.

I United States Patent 1 1 3,560,811

[72] lnventor George Farago 3,226,616 12/ 1965 Seiden 317/249(T) 206 E. 37th St.. Brooklyn. N.Y. 11203 3239730 3/1966 Farago 317/249(T) [2]] Appl. No 828,971 3,268.784 8/1966 Harwood 317/249(T) [22] Filed May 29, 1969 3,336,515 8/1967 Seiden et al. 317/249(T) Patented 1971 Primary Examiner-E. A. Goldberg Attorney-Greene & Durr [54] VARIABLE CAPACITORS Claims, 10 Drawing Figs.

317/ 1 ABSTRACT: In the variable capacitors of the coaxial type [51 l where a tubular electrode is moved crew or imilar action Fleld 0f 3 l to engage more o less a stationary electrode and dielectric is 249T 25 1 between the electrodes, a spring-stressed means is provided to 56 R f establish direct contact between the movable electrode and a I l e erences cued circuit, which said spring-stressed means can be also the rota- UNITED STATES PATENTS tion restraining element and the positive stop for the movable 2.601826 8/1952 Barnes 317/249(T) electrode.

16 IO 13 I5 20 I b 54 b L "r;

I BI 40 5' I 41 a7 56 so 42 VARIABLE CAPACITORS This invention relates to an improved variable capacitor of the coaxial type having a tubular housing with a stationary electrode fixed axially to the housing from one end thereof. a movable electrode to be moved axially of the housing to closely engage more or less with the coaxially positioned stationary electrode. dielectric between the electrodes. the housing including at least a ring of insulating material to insulate the stationary electrode from the movable electrode. and screw means adapted to move the electrode This type of variable capacitor is also described in my US. Pat. No. 3,239,730, especially in FIGS. 12 thereof. In such devices, the connection of the movable electrode to the circuit is established mainly through the screw means and through the metal portion of the housing. Thus, the extent or pressure of contact, and the length between the movable electrode and the screw and/or the metal portion of the housing varies from time to time depending on the position of the movable electrode with respect to the screw or the housing so that the series resistance, created by the screw and the contacts, depends on the contacts therebetween. It is well known that the increase of the series resistance of a capacitor decreases the merit (Q factor) of the capacitor and limits the usefulness of the device with increasing high frequency.

Among the objects of the present invention is to provide a high Q variable capacitor for extended frequency range, in which the pressure and area of contact between the movable electrode and the terminal of the unit is substantially constant and the RF current path is the shortest for all positions of the movable electrode, and wherein the adjusting screw is not involved in the contact path.

Among other objects of the invention is to provide a variable capacitor of the type described, in which the force required to move the movable electrode is constant and not excessive, regardless of the position of said electrode.

The objects of the invention are attained by providing an annular arrangement of one or more spring-stressed contact elements within the housing or casing of the capacitor, to make direct frictional contact with the movable electrode as it moves toward the stationary electrode and to make contact with the circuitry. Said frictional contact elements are preferably made of springy material, for example beryllium copper or the like, and can be formed as a hollow body containing one or more longitudinal slots to provide flexible sectors to engage the outer surface of the movable electrode. When the annular arrangement of spring-stressed contact elements is formed of the tubular metal part of the housing which is slotted at the end, a metal ring member with tenninal projection is provided, surrounding the contact elements, for sealing to the insulating part and to the metal part of the housing, and providing also contact to the circuitry. The said springstressed contact elements can be formed, as said before, as an integral part of the interior or end portion of the metal tube which forms part of the housing, or can be formed as an integral part of the terminal ring member. Rotation of the movable electrode can be prevented, for example, by flattening at least a portion of the circumference of the movable electrode, or making the electrode, or a part of it, with a polygon or other noncircular cross-sectional shape, or with keyway configurations and by making at least a part of the housing or terminal ring with a shape to complement the noncircular cross-sectional shape of the electrode. The axial movement of the movable electrode can also be stopped by the terminal ring.

Further objects and advantages of the invention will be apparent from the following detailed description of the embodiments of the invention when considered in connection with the accompanying drawings, in which:

FIG. 1 is an axial cross-sectional view of a capacitor made according to the invention;

FIG. 1a is a cross-sectional view taken on line .a-a of FIG. 1;

. lb is a cross-sectional view taken on line b-b of FIG. 1-; FIG. 1c is a cross-sectional view taken on line c-c of FIG. 1; FIG. 2 is a view, similar to FIG. 1, but partly cut away, of a modified form of the device;

FIG. 2A is a view taken on line A-A of FIG. 2:

FIG. 2B is a view taken on line 8-8 of FIG. 2;

FIG. 3 is a view, partly cut away, showing an alternate form of the device;

FIG. 3a is a view, partly cut away, of a movable electrode, with a separate guide ring;

FIG. 3b is a view taken on line A-A of FIG. 3a.

The device shown in FIG. 1 comprises a stationary electrode 10 held at the upper end by a metal cap 11, which provides a terminal 12 for said stationary electrode. The electrode 10 extends downwardly from the cap 11, is coated with a dielectric material 16 (Teflon, for example), and is surrounded by the insulating sleeve 13, sleeve 13 being a part of the housing of the device shown. The cap 11 is solder sealed to the sleeve 13 at 14, and insulating sleeve 13 is also solder sealed at its lower edge, to the ring 20 at 15. Ring 20 is of conducting metal and provides a terminal 21 for outside connection to a circuit. Ring 20 has an interior collar 22 adapted to fit within the flange 31 of the lower metal tube 30. Below the flange 31, as shown in FIG. 1b, the tube 30 is a solid tube. At the lower end of the tube 30, the opening is concentrically enlarged to form a shoulder 35, and at the very end, the opening is enlarged again to provide the shoulder 36 and the thin rim portion 37, which may be swedged over as shown in FIG. 1. Shoulder 35 provides a seat for the thrust washer 40 and a spring washer 41 is provided between cap 42 and flanges 51 of screw means 50.

Screw 50 extends substantially the full length of the tubular metal portion 30 of the housing and is rotatably held in said part 30, while being prevented from moving axially by said peripheral flanges 51, said spring washer 41 and cap 42.

Projecting down from the collar 22 into the enlargement formed by said flange 31 are a plurality of spn'nglike sectors 23, 24, 25, 26 (see FIGS. 1 and 1a), which in the form shown in FIG. 1, are integrally formed with and as projections from the collar 22. These sectors 23-26 are stressed to bear against the outside of movable electrode 80.

The movable electrode includes the cylindrical body 80, projecting from which are the key means 8384 and at its base, there is attached the internally threaded closure 81 which meshes with the threaded portion 52 of screw 50. Said two projecting key means 83, 84 (see FIGS. 1a, 1b, 1c), are adapted to ride in the slots 33, 34 of the ring terminal 20 and prevent the electrode from rotating. The closure 81 acts as a positive stop of the movable electrode at the sectors 2326.

Thus, the slotted head of screw 50 is always in the same position, regardless of the position of movable electrode 80, and the contact between electrode 80 and ring tenninal 20 is substantially constant, as it is always determined by the contact area of the spring pressed sectors 2326.

In the form of device shown in FIG. 2, the ring terminal portion 20' has a flange 27 adapted to surround the housing 30, which has a uniform outside tubular shape, but is provided with a pair of longitudinal internal channels 33, 34. The ring terminal 20 is provided with a collar 22 from which project the spring fingers 23, 24', 25', 26', which are tensioned to bear against the outer surface of movable electrode 80'. The electrode 80' is provided at the lower end with a pair of keyshaped projections 83', 84', matching channels 33, 34 which prevent the electrode 80 from rotating when the screw means 52 is rotated. The cylinder 10' is coated intemally with a dielectric layer 16; of Teflon, for example.

FIG. 3 shows the structure of a somewhat different ring terminal and housing, which can be substituted for the ring 20 or 20' and housing 30 or 30 of FIG. 1 or 2. In FIG. 3, the ring 20' is tightly fitted and united to housing 30" to provide good electrical conductivity between said housing 30" and said ring 20". Housing 30" contains a pair of longitudinal slots 33 (only one shows, like the housing of FIG. 2, but the upper end of said housing is slotted at 61, 62, 63, etc., and the finger or sectors between the slots are reduced in thickness so as to form the spring pressed fingers 23", 24", etc. Also, the movable electrode of FIG. 2 can be replaced by the electrode 80" of FIGS. 3a and b. Said electrode 80" having an annular groove at its lower end into Wl'llCll lS compressed a spring containing projections 8181" l claim:

1. ln a variable capacitor of the coaxial type, comprising a tubular housing with a fixed stationary electrode at one end thereof. a movable electrode member adapted to be moved axially from the other end of said housing to positions engaging more or less with the stationary electrode, dielectric between said electrodes, rotatable means operating the movable electrode member from said other end of the housing, said housing including a first part extending beyond the interior limits of the stationary electrode, and a second part surrounding the major part of the movable electrode when the latter is in its position furthest from the stationary electrode, said first part including means to insulate the first part from the second part, the improvement comprising:

a contact ring terminal member jointed and hermetically sealed between the first and second parts of said housing; said contact ring terminal member being electrically connected to at least two, annularly arranged, electrically conducting, spring-stressed .contact elements projecting inwardly beyond the internal wall of the second part of said housing; said movable electrode member comprising an electrode portion adapted to slide freely within said second part of the housing and an end portion adjacent the free end of said housing provided with at least one projection adapted to fit snugly and slidably within said second part of this housing, said electrode portion making sliding contact with the stressed, contact elements whereby the end portion of said movable electrode member and the electrically conducting spring-stressed contact elements cooperate to guide the movable electrode in a straight axial direction; and

said end portion of said electrode member acting as a stop when said end portion approaches the contact ring terminal member.

2. The variable capacitor as claimed in claim 1 wherein the end portion of said movable electrode and the internal wall of the second part of said housing comprise a key and slot arrangement to prevent rotation of the movable electrode member with respect to said housing.

3. The variable capacitor as claimed in claim 1 wherein the electrode portion of said movable electrode is noncircular in cross section and wherein the contact elements of the ring terminal member is shaped to cooperate with said noncircular electrode portion to prevent rotation of the electrode member with respect to the housing when the rotating means operating the movable electrode means is operated.

4. The variable capacitor as claimed in claim 3 wherein the electrode portion of said electrode member comprises at least one elongated projection which slides snugly in a space between two of the spring-pressed contact elements.

5. The variable capacitor as claimed in claim 1 wherein said movable electrode member is formed from a tubular body of substantially uniform cross-sectional size but is provided with at least one slot adjacent the end thereof, projecting means having a noncircular outer configuration inserted in said slot to form said end portion, said second part of the housing including an interval longitudinal, irregularity to match the projecting means in said slot. 

2. The variable capacitor as claimed in claim 1 wherein the end portion of said movable electrode and the internal wall of the second part of said housing comprise a key and slot arrangement to prevent rotation of the movable electrOde member with respect to said housing.
 3. The variable capacitor as claimed in claim 1 wherein the electrode portion of said movable electrode is noncircular in cross section and wherein the contact elements of the ring terminal member is shaped to cooperate with said noncircular electrode portion to prevent rotation of the electrode member with respect to the housing when the rotating means operating the movable electrode means is operated.
 4. The variable capacitor as claimed in claim 3 wherein the electrode portion of said electrode member comprises at least one elongated projection which slides snugly in a space between two of the spring-pressed contact elements.
 5. The variable capacitor as claimed in claim 1 wherein said movable electrode member is formed from a tubular body of substantially uniform cross-sectional size but is provided with at least one slot adjacent the end thereof, projecting means having a noncircular outer configuration inserted in said slot to form said end portion, said second part of the housing including an interval longitudinal, irregularity to match the projecting means in said slot. 